Currently, an optical fiber access network mainly adopts a PON technology. FIG. 1 is a schematic view of the structure of an optical access network (OAN) system. The OAN system includes a customer premises network (CPN), an access network (AN) and a service node function. In the AN, an adaptation function (AF) is an optional equipment, which mainly provides mutual conversion between an optical network unit (ONU)/optical network terminal (ONT) interface and a user network interface (UNI). The AF may also be built in the ONU, and in this case, the reference point “a” in FIG. 1 can be omitted. The AF may also be arranged behind an optical line termination (OLT) to provide mutual conversion between an OLT interface and a service node interface (SNI). The AF can not only be regarded as a function of the CPN, but also regarded as a function of the AN. The main network elements of the CPN and the AN include the OLT, an optical distribution network (ODN), the ONU/ONT, and the AF. T is a reference point for the UNI interface, and V is a reference point for the SNI interface. The OLT provides a network interface for the ODN, and is coupled to one or more ODNs. The ODN provides a transmission means for the OLT and the ONU/ONT. The ONU/ONT provides a user side interface for the OAN, and is coupled to the ODN. A broadband network gateway (BNG) is located at a metropolitan area network (MAN) side, and is coupled to the OLT.
A conventional PON topology is of a star structure. That is, one OLT is coupled to multiple ONU/ONTs through the ODN, and interconnection is not supported between the OLTs. This star structure causes the OLT to be the bottleneck of the PON, and a single point failure occurs easily. Once an OLT fails, breakdown of links associated thereto occurs and the network is greatly affected.